The main objective of this renewal application is to define, at the molecular level, the antigenic sites on SV40 T antigen recognized by the cytotoxic T lymphocytes (CTL) in association with self coded major histocompatibility complex class I or class II glycoproteins. We have identified at least three distinct CTL recognition sites in the amino terminal half and one site in the carboxy terminal half of SV40 T antigen. Using CTL clones and SV40 deletion mutants, we are now proposing to, (1) determine the identify of amino acids in CTL recognition sites on T antigen and the influence of amino acids within the sites on CTL recognition in association with H-2 antigens; (2) analyses of antigenic loss variants that have escaped CTL mediated lysis for alteration in SV40 T antigen CTL recognition antigenic sites; (4) investigate the nature of T antigen recognized by CTL; and (5) study the contribution of individual antigenic sites to CTL mediated response. The approach utilized here will allow us to relate the role of SV40 T antigen in transformation and in inducing a CTL immune response to the antigenic sites on SV40 T antigen in the host undergoing oncogenesis.